Fig. 5.

Agonist effects of diadenosine 5′,5‴-P¹,P⁴-tetraphosphate (Ap₄A) analogs on P2X1-mediated entry of extracellular Ca²⁺. Increasing concentrations of Ap₄A analogs were added to FLUO-4-loaded platelets, and the change in FLUO-4 fluorescence was measured by flow cytometry. The results shown are mean ± standard error of the mean normalized to the response to adenosine 5′-(β,γ-methylene)triphosphate (β,γ-CH₂-ATP) (20 μM) alone; compound 3 was evaluated at only 1 and 100 μM. The results for Ap₄A and compounds 1, 2 and 4 are from four to eight independent experiments. Compounds: 1, diadenosine 5′,5‴-P¹,P⁴-dithiotetraphosphate; 2, diadenosine 5′,5‴-P²,P³-chloromethylenetetraphosphate; 3, diadenosine-5′,5‴-P¹-thio-P²,P³-chloromethylenetetraphosphate; 4, diadenosine-5′,5‴-P¹,P⁴-dithio-P²,P³-chloromethylenetetraphosphate.